Due to T39338: $wgTranslateBlacklist of zh-* on metawiki translation of zh-* sub-variants are blocked. However this is needed as zh banners are not displayed for zh-* users.
Two ways to fix this:
0) Revert T39338 or modify it to unblock zh-hans and zh-hant
- Allow CNBanners to ignore the blacklist or have a separate set
- Language conversion for CNBanners (ideal solution)
Currently change in T39338 pretty much breaks the translation workflow as the only way around it is for a translator to ask an administrator to edit the MediaWiki message.